Gastric protein digestion of goat and cow milk infant formula and human milk under simulated infant conditions.

The protein digestion kinetics of goat milk infant formula (GMF) is previously shown to be more comparable to that of human milk (HM) than cow milk infant formula (CMF). To evaluate whether gastric behaviour contributes to differences in protein digestion kinetics, fresh HM, a GMF and a CMF were subjected to in vitro gastric digestion simulating infant conditions. Coagulation behaviour, particle size distribution and viscosity of the digesta were evaluated. After centrifugation of the digesta, total solids and protein distribution, and protein hydrolysis in the cream, serum and pellet fraction were investigated. The GMF and CMF were in general similar with respect to physicochemical and protein breakdown properties. However, a number of notable differences in physicochemical behaviour were observed, which may contribute to faster initial protein digestion of GMF. HM behaved differently from both formulas. These differences provide new insights into the possibilities for improvement of infant formulas.

A comparison of the lubrication behavior of whey protein model foods using tribology in linear and elliptical movement.

Lubrication is an important factor in the sensory evaluation of food products. Tribology provides a theoretical framework and instrumental methods for evaluating frictional properties between two moving surfaces and the lubrication behavior of products between these surfaces. Relating frictional measurements to sensory properties detected during oral processing requires careful and pertinent choices in surface materials and testing conditions. The aims of this study were to investigate: (a) differences in lubrication behavior of a range of food textures and (b) the differences between linear and elliptical movement and added saliva to understand the contribution of food structure to friction. Six whey protein model food samples, ranging in texture from fluid to semisolid to soft solid, were analyzed using a pin on disk tribometer to determine the coefficient of friction (COF) across a range of sliding speeds. The samples were analyzed in their initial form and post-oral processing (n = 4) in both linear and elliptical movements. Elliptical movement slightly decreased coefficients of friction and extended the shape of the friction curve. Increases in test food viscosity decreased the COF but differences in viscosity were not apparent when test foods were mixed with saliva. Data correction for viscosity shifted the friction curves horizontally, indicating that lubrication had a greater impact upon friction than viscosity. This study provides initial insights for further comparison of linear and elliptical movement with a variety of sample compositions. PRACTICAL APPLICATIONS: Sensory perception of smoothness and creaminess are often major contributors to overall hedonic food liking and are a major reason why products high in fat and sugar are more highly preferred over other foods. These parameters are influenced by friction and lubrication between the tongue, palate, teeth, food products, and saliva during oral processing. Tribology provides an instrumental method to evaluate friction between moving surfaces that mimic oral surfaces and the lubrication behavior of foods. Trends in frictional measurements can be correlated with sensory ratings of the same foods to better understand why preferences exist for certain foods or food compositions and how to effectively improve the acceptability and enjoyment of healthier foods.

Bolus matters: the influence of food oral breakdown on dynamic texture perception.

This review article focuses on design of food structure, characterisation of oral processing by boli characterisation and dynamic texture perception. Knowledge of the food properties governing bolus formation and bolus properties determining temporal changes in texture perception is of major importance. Such knowledge allows academia to better understand the mechanisms underlying texture perception and food industry to improve product texture. For instance, such knowledge can be used for developing foods with desired texture perception that fit in a healthy diet or that are customized to specific consumer groups. The end point of oral processing is the formation of a safe-to-swallow bolus. The transitions of solid and soft solid foods into bolus are accompanied by tremendous modifications of food properties. The review discusses dynamic changes in bolus properties resulting in dynamic changes of texture perception during oral processing. Studies monitoring chewing behaviour are discussed to complement the relationships between bolus properties and dynamic texture perception. We conclude that texture perception evolves over mastication time and depends on food properties, such as mechanical properties, mainly in the beginning of oral processing. Towards the middle and end of oral processing, bolus properties depend on food properties and explain texture perception better than food properties.

Formation Dynamics of Oral Oil Coatings and Their Effect on Subsequent Sweetness Perception of Liquid Stimuli.

Knowledge of the formation of oral coatings and their influence on subsequent taste perception is necessary to understand possible taste-masking effects by oil coatings. This study investigated (a) the dynamics of the formation of oral oil coatings formed by o/w emulsions and (b) the effect of oral oil coatings on subsequent sweetness perception of sucrose solutions. In vivo fluorescence was used to quantitate the oil fraction deposited on the tongue after oral processing of oil-in-water emulsions for different times. A trained panel evaluated sweetness perception of sucrose solutions after orally processing the emulsions. The oil fraction reached its maximum value within the first 3 s of oral processing. The oil fraction did not significantly affect subsequent sweetness perception of sucrose solutions. It is suggested that the oil droplets deposited on the tongue did not form a hydrophobic barrier that is sufficient to reduce the accessibility of sucrose to taste buds.

Protein-polysaccharide interactions to alter texture.

The sensory perception of texture is an important contributor of our general appreciation of foods. Food texture is mainly described in terms of mouthfeel and afterfeel attributes. The role of oral processing in the perception of texture and the role of microstructure therein have been reviewed regularly over recent years (Chen & Engelen 2012, Foegeding et al. 2011, Stieger & van de Velde 2013) and are not, therefore, addressed in this review. The scope of this review relates to the molecules that underlay the texture of foods. Protein, carbohydrate, and fat are the major structuring components in foods. In this review we focus on the physical interactions between proteins and polysaccharides that form the basis for the microstructure and texture of these foods. In general, food products are classified in four categories by their sensory and rheological properties: liquids, semisolids, soft solids, and hard solids (van Vliet et al. 2009). These four categories provide a useful classification framework, although they are not precisely defined by specific rheological properties. The current review focuses on semisolid and soft-solid foods.

Properties of oil/water emulsions affecting the deposition, clearance, and after-feel sensory perception of oral coatings.

The aims of this study were to investigate the influence of (i) protein type, (ii) protein content, and (iii) viscosity of o/w emulsions on the deposition and clearance of oral oil coatings and after-feel perception. Oil fraction (m(oil)/cm(2)(tongue)) and after-feel perception differed considerably between emulsions which do not flocculate under in mouth conditions (Na-caseinate) and emulsions which flocculate under in mouth conditions (lysozyme). The irreversible flocculation of lysozyme stabilized emulsions caused slower oil clearance from the tongue surface compared to emulsions stabilized with Na-caseinate. Protein content had a negative relation with oil fraction for lysozyme stabilized emulsions and no relation for Na-caseinate stabilized emulsions immediately after expectoration. Viscosity differences did not affect oil fraction, although the presence of thickener decreased deposition of oil on tongue. We conclude that after-feel perception of o/w emulsions is complex and depends on the deposited oil fraction, the behavior of proteins in mouth, and thickeners.

The structure of kappa/iota-hybrid carrageenans II. Coil-helix transition as a function of chain composition.

This paper describes the effect of the kappa/iota-ratio on the physical properties of kappa/iota-hybrid carrageenans (synonyms: kappa-2, kappa-2, weak kappa, weak gelling kappa). To this end, a series of kappa/iota-hybrid carrageenans ranging from almost homopolymeric kappa-carrageenan (98 mol-% kappa-units) to almost homopolymeric-carrageenan (99 mol-% iota-units) have been extracted from selected species of marine red algae (Rhodophyta). The kappa/iota-ratio of these kappa/iota-hybrids was determined by NMR spectroscopy. Their rheological properties were determined by small deformation oscillatory rheology. The gel strength (storage modulus, G') of the kappa/iota-hybrids decreases with decreasing kappa-content. On the other hand, the gelation temperature of the kappa-rich kappa/iota-hybrids is independent of their composition. This allows one to control the gel strength independent of the gelation or melting temperature. The conformational order-disorder transition of the kappa/iota-hybrids was studied using optical rotation and high-sensitivity differential scanning calorimetry. High-sensitivity DSC showed that the total transition enthalpy of the kappa/iota-hybrids goes through a minimum at 60 mol-% kappa-units, whereas for the mixture of kappa- and iota-carrageenan, the total transition enthalpy is a linear function of the composition. With respect to the ordering capability, the kappa/iota-hybrid carrageenans seem to behave as random block copolymers with length sequence distributions truncated from the side of the small lengths. Intrinsic thermodynamic properties (e.g., transition temperature and enthalpy) of kappa- and iota-sequences in these copolymers are close to those of their parent homopolymers. The critical sequence length for kappa-sequences is 2-fold of that for iota-sequences.

The revised NMR chemical shift data of carrageenans.

A new set of (13)C and (1)H NMR chemical shifts of most common carrageenan types is given relative to DSS as the internal standard according to the IUPAC recommendations. Moreover, the chemical shifts of characteristic signals for pyruvate acetal and floridean starch are reported. Additionally, chemical shifts of common internal standards, such as methanol, DMSO and acetone, were measured at different temperatures and pH values.

Gelation of casein-whey protein mixtures.

Heated milk consists of a mixture of whey protein-coated casein micelles and soluble whey protein aggregates. The acid-induced gelation properties of heated milk are consistently different from those of unheated milk--i.e., a shift in gelation pH, stronger gels, and a different microstructure of the gels. In this study we investigated the role of the different fractions of denatured whey proteins on the acid-induced gelation, the gel hardness, and the microstructure. Both whey protein fractions contribute to the observed shift in gelation pH, although by a different mechanism. Obtaining gels with high gel hardness occurs most effectively when all denatured whey proteins are present as whey protein aggregates. It was observed that disulfide bridge exchange reactions during the acid-induced gelation at ambient temperature play an important role for both whey protein fractions. Additionally, disulfide interactions seem to occur between the aggregates and the casein micelles during the gel state. In this study, we show the development of a new approach for confocal scanning laser microscopy measurements--i.e., separate staining of the proteins in milk. By using this method, we were able to determine that, although whey protein aggregates are not linked to the casein micelles, they nevertheless gel at the same moment. This work adds to a better understanding of the role of denatured whey proteins during acid-induced gelation and could improve the effective use of whey proteins.

Coil-helix transition of iota-carrageenan as a function of chain regularity.

A series of iota-carrageenans containing different amounts of nu-carrageenan (0-23 monomer %) have been prepared from neutrally extracted carrageenan of Eucheuma denticulatum. nu-Carrageenan is the biochemical precursor of iota-carrageenan. The conformational order-disorder transition and rheological properties of these carrageenans were studied using optical rotation, rheometry, size exclusion chromatography coupled to multiangle laser light scattering, and high-sensitivity differential scanning calorimetry. The helix forming capacity of iota-carrageenan turns out to decrease monotonously with increasing amount of nu-units. In contrast, the rheological properties of iota-carrageenan are remarkably enhanced by the presence of a small amount of nu-units, yielding a maximum twofold increase in G' at 3% nu-units. It is concluded that the structure-forming capacity of iota-carrageenan, containing a small amount of nu-carrageenan, is significantly higher than that of pure iota-carrageenan. This phenomenon is explained in terms of the balance between the helical content and the number of cross-links between chains, taking into consideration the fact that nu-units introduce "kinks" in the chain conformation enabling neighboring chains to connect. Increasing amounts of nu-units increase the number of cross-links in the network, resulting in increased gel strength. On the other hand, a reduced length of the helical strands weakens the cross-links between the different chains and, consequently, the gel.